Scala example source code file (WeakReference.scala)

This example Scala source code file (WeakReference.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

anyref, none, option, referencequeue, referencewithwrapper, referencewrapper, some, t, weakreference, weakreferencewithwrapper

The WeakReference.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */


package scala.ref

/**
 *  A wrapper class for java.lang.ref.WeakReference
 *  The new functionality is (1) results are Option values, instead of using null.
 *  (2) There is an extractor that maps the weak reference itself into an option.
 *  @author Sean McDirmid
 */
class WeakReference[+T <: AnyRef](value: T, queue: ReferenceQueue[T]) extends ReferenceWrapper[T] {
  def this(value: T) = this(value, null)
  val underlying: java.lang.ref.WeakReference[_ <: T] =
    new WeakReferenceWithWrapper[T](value, queue, this)
}

/** An extractor for weak reference values */
object WeakReference {

  /** Creates a weak reference pointing to `value` */
  def apply[T <: AnyRef](value: T) = new WeakReference(value)

  /** Optionally returns the referenced value, or `None` if that value no longer exists */
  def unapply[T <: AnyRef](wr: WeakReference[T]): Option[T] = {
    val x = wr.underlying.get
    if (x != null) Some(x) else None
  }
}

/**
 *  @author Philipp Haller
 */
private class WeakReferenceWithWrapper[T <: AnyRef](value: T, queue: ReferenceQueue[T], val wrapper: WeakReference[T])
  extends java.lang.ref.WeakReference[T](value, if (queue == null) null else queue.underlying.asInstanceOf[java.lang.ref.ReferenceQueue[T]]) with ReferenceWithWrapper[T]